A stack mold comprises, a center and two outside mold sections which open and close relative to one another to expose the mold cavities for parts ejection. In a typical 2.times.2 or 4.times.4 set up the mold cavities are offset from the center of the middle mold section outwardly around the sprue bar which provides a flow path for the injection of plastic to the middle mold section which then divides into branches outwardly to the individual mold cavities.
The above arrangement is objectionable for what is known as a 1 by 1 stack mold, which has back to back mold cavities positioned centrally of the middle mold section. This does not allow the central sprue bar fitting which would have to completely pass through one of the mold cavities to get to other mold cavity.